Radio receiver



Oct. 23, 1951 A. PREISMAN 2,572,053

RADIO RECEIVER Original Filed May' 7, 1943 I i I f/o/F/zo/vm BY I afa fer/0N i I g /a K Wan/ f J L l '7 RADIO RECEIVER Albert Preisman, Silver Spring, Md., assigner to Federal Telephone and Radio Corporation, New York, N. Y., a corporation of Delaware Original application May 7, 1943, Serial No. 485,971. Divided and this application August 6, 1945, Serial No. 609,217

Claims. (Cl. Z50-20) The present invention relates to radio reception, and more particularly to apparatus for controlling the reception of signals and picturing them on the screen of an oscilloscope.

This is a division of my copending application for Scanning Control Means, Serial No. 485,971, led May 7, 1943, now abandoned.

I t is often advantageous, in a radio receiving system including an oscilloscope, to scan a portion of the spectrum and to locate accurately any frequency in that range. It is therefore desirable to provide an automatic control for the receiving circuit that will provide intervals of scanning separate from intervals of Xed tuning, so that the signals received during these intervals may then be separately pictured on the screen of the oscilloscope.

. vThe present invention features an improved apparatus for accomplishing the above results, and is a further development of the idea disyclosed in my copending application, Serial No. 485,970, filed May 7, 1943, now U. S. Patent No. 2,450,018 issued September -28, 1948, for Radio Monitoring System.

AAnother object of the present invention is to control the deiiection of an oscilloscope beam so as vto separate the picture of the scanned signals appearing on the screen from the picture of the tunedsignals.

' The invention has as a still further object the provision of mechanical means for varying the inductance of a tuning coil forming a part of a receiving circuit, this means including a shield of conducting material which is periodically inserted between two windings of the coil to cause the receiver incorporating the coil to receive varying frequencies during periods when an irregularly-shaped portion of the shield is passing between the windings to vary the inductance of the coil, and to receive a single frequency during periods when a regularly-shaped portion of the shield (or no portion of the shield) is passing between the windings to hold the inductance of the coil constant.

'f Other objects and advantages will be apparent from' the following description of a preferred embodiment of the invention and also from the accompanying drawings, in which:

Fig. 1 is a schematic and block diagram of a radio receiving circuitv in accordance with the present invention;

2 is a sideview of the inductance-varying device indicated inFig. 1; and '1 Fig.l 3- is 'a set 'ofcurves illustrating the operation'of the' 'circ1 1itjof Fig. 1.

In Fig. 1 is shown a receiver and detector I2, which includes a rst tuning circuit portion I0. The output of receiver and detector I2 is applied through an amplifier I4 to the vertical deflection plates I5 of an oscilloscope having a screen- I6. A square wave generator isalso shown, operated by a motor I8. A portion of the square wave output of generator 20-is fed to the vertical dep flection plates I5 of the oscilloscope, and the remaining portion is applied to the horizontal deflection plates 2| of the oscilloscope throughja wave generator 22. 1

In the tuning circuit portion I0 of Fig. 1 is illustrated a pair of coil forms 23 and 25 lying along the same longitudinal axis. 0n coil form 23 is wound a primary winding P and a portion of a secondary winding S1. On coil form 25 is wound anothersecondary winding portion S2. S1 and S2 are connected in series as shown.

An insulating .disc 24 'is rotatably mounted between coil forms 23 and 25. This disc is designed to be rotated by motor I8 synchronously with the operation of square wave generator 20. The rotation of disc 24 may either be clockwise or counterclockwise as may be desired depending upon whether a decreasing or an increasing frequency scanning is preferred.

In a preferred arrangement, the faceof disc 24 has positioned thereon two strips 21 and 29 (Fig. 2) of conducting material, such as copper sheet. These strips 21 and 29 are designed to pass alternately between coil forms 23 and 25 upon rotation of disc 24 by motor I8 to act as partial shields between windings Si and S2, thus reducing the mutual inductance between these windings and hence the total inductance of the overall secondary. v

As will be seen from Fig. 2, insulating disc 24 is divided into two sections v, c of approximately each. Section c includes strip 21, which, is; irregular in cross-section so as to present between windings S1 and S2 upon rotation of disc 24 an area of conducting material constantly varying from a minimum to a maximum value (for the clockwise direction of rotation assumed). This resultsy in a variation inthe inductance of S1 and S2 from a maximum to a minimum value.

On the other hand section c includes strip 29, which is regular in cross section so as to present between windings S1 and S2 upon rotation of disc 2.4 a constant area of conducting material, thus holding the inductance of S1 and S2 substantially fixed. If strip 29 has half the cross section of strip 21 at its widest end, the inductance of Si, S2 will be fixed during half-revolution at a value intermediate between the minimum and maximum values of inductance produced by strip 2'I during half-revolution v.

Thus the receiver-detector I0, I2 of Fig. 1 can be made to scan, or receive varying frequencies, during'half-revolution v of disc 24, and be made to tune or receive a single frequency, during half-revolution c. A variable condenser 26 is connected in parallel with S1, S2 to preselect the scanning range desired.

The above operation results in an alternate scanning tuning output of the receiver-detector I0, I2. The variation in frequency with time for the design of the strips chosen by way of example is illustrated in Fig. 3 (A) ti representing the time consumed during half-revolution v of disc 24, and tz representing the time consumed during half-revolution c.

At the beginning of half-revolution v (if the disc 24 is positioned relative to coil form 23 as shown in Fig. 2), the coils are still shielded by a portion of strip 29. Upon rotation of the disc, the insulated section d enters the gap between Si and S2, this section having a length approximately equal to the diameter of the coil forms 23 and 25. The mutual inductance between the coils will thus increase until the coil form 23 is completely intercepted by the insulating section d, at which time the mutual inductance of Si, S2 will have a maximum value. A5 the smaller end of strip 21 now enters the gap between S1 and S2, the inductance decreases steadily until completion of half-revolution u. As half-revolution c begins, the inductance increases unt-il the coils are separated solely by constant area strip 29, at

which point the increase terminates, and the inductance remains fixed during the remainder of half-revolution c back to the original starting point. It will thus be seen that halt-revolution 'u does not result in a constantly decreasing mutual nductance between the coils during the entire period t1, but that an intermediate or cha-ngeover, period g is present during which an increase in inductance occurs. Similarly, half-revolution -c does not result in a constant inductance during the entire period t2, but a change-over period e is present during which the inductance varies. Time interval e corresponds to f of Fig. 2; time interval y to d of Fig. 2. These change-over periods produce undesirable variations in the traces on the screen of the oscilloscope, and are eliminated in one of the conventional manners hereinafter mentioned; In Agraph A of lFig. 3, the variations in frequency received is assumed to be inversely proportional tothe variation in mutual inductance of S1, S2.

In order to picture the result of the above described scanning-tuning signal 'reception on the screen IS of the oscilloscope, the following procedure may be followed. A square wave generator 20 is operated by motor I8 as shown in Fig. 1, the wave output of this generator being shown in Fig. 3 (B). The period of this square wave B is the same as the period of tuning variation A, that is, (nfl-t2). In other words, one rotation of disc 24 equals in time one cycle of square wave B, due to their common control means I6. -A possible method of generating square wave B would utilize a rotating switch mounted on `the driving shaft of motor I3, and have a brush connected to a suitable D C. supply, such as'the plate circuit of the receiver and detector I0, 'I`2.

`Also produced in the lcircuit of Fig. Vl is atriangulaiivave C, `this wave being integrated or keyedin a well-known manner from square Wave B by the wave generator 22, as shown. The periods of waves B and C are similar, as shown in Fig. 3.

Wave B, upon which is superimposed the signal output of the receiver I6, I 2 representing frequencies as shown in `Fig. 3 (A) applied to the vertical deflection plates of the oscilloscope. Wave C is applied to the horizontal deection plates, suitable amplifying means (not shown) being employed if necessary.

The resulting picture on the screen I6 of the oscilloscope is shown in Fig. 1. Trace EF covers the varying frequencies received during the scanning half-revolution 1J of disc 24, and appears on the upper half of screen I6 due to the high potential period MN of vertical deflection wave B. The portion JK of triangular wave C sweeps across the screen I6 this portion MN of wave B on which is superimposed the scanning output of the amplier I4 during half-revolution o of disc 24.

Trace GH is the reverse sweep due to'portion KL of horizontal deection wave C. During this time the equal-area conducting strip 29 is passing between Si, S2 and the receiver portion Ig is tuned to a single frequency. Also due to lower potential portion RW of vertical deflection Wave B, trace GH is on the lower half of oscilloscope screen IS.

Thus trace GH should be a picture of the time wave shape of the signal which happens to be of the frequency to which the receiver is tuned during t2.

Dotted lines FG, HE represent the instant downward and upward shifts, respectively, oc7 curi-ing at the ends of the half periods of wave B.

The undesirable portions of traces El and QH occurring during intervals e and g, wave A, as a result of the portions d and f of the disc construction may be eliminated from the visual area of screen I6 by one of several conventional methods. These include a suitable covering of the outer edges of screen I6 by opaque material so that only the desired parts of the .pictures 4will be observed, a decrease in horizontal sweep voltage at the beginning of intervals t1 and t; so that little, if any, sweep occurs during intervals e and g, or, to control the grid inthe ,oscil loscope to blank the beam during intervals e and y.

Through manual adjustment of the condenser 26, any single frequency may be selected Afrom the range vpictured as a result of the changing inductance of S1, S2, .and .transierred from the upper to the lower half of .thepscih loscope screen I6 to permit close inspection of its characteristics.

While Ihave described-above .the principles of my invention in connection with specinc apparatus, it is .to be clearly understood that .this description is inadeonly by way of example and not as .alimitationonthescope of my inyention.

claim: l

.1. In a ,radio circuit including a receiver and an Voscilloscope having a screen, means fp incyclh cally tuning said Areceiver -`to scan a given girequency band to derive the signals thereof ,d ing a part .cfa given cycle, means Qperative ,alternately with said rst-mentioned means gior maintaining said rcceiir receptive to wsignals gf xed frequency duringanotherpart of said cycle, means for applying ,said received scanned signals and Asaid Areceived fixed Afrequencysignals to said oscilloscope to produce ,trace indications ,on the screen thereof, means for separating the traces corresponding to said received fixed frequency signals and said received scanned signals on the screen in synchronism with their respective occurrences during said cycle.

2. The radio circuit of claim 1, in which-said rst mentioned means comprises means for uniformly tuning said receiver in a given direction during substantially half of said cycle.

3. In a receiver circuit, an oscilloscope comprising separate deflection elements, a receiver, rst means for sequentially and cyclically tuning said receiver to scan a given frequency band, means' for tuning said receiver to be receptive to signals of a single frequency included in said frequency band, means for alternately rendering eective the said first and second means at a given rate, means for applying the received signals to one set of deflection elements, means for producing a square wave at said given rate, means for applying said square wave to said one set of deflection elements, means for producing a source of scanning waves at said rate, and means lconnecting said source to said other set of deflection elements.

4. In a circuit including a receiver on a cathode ray oscilloscope having a screen and deiiection element, means cyclically scanning a given frequency band over a given period of the operating cycle of said receiver, means coupled to said receiver and said deflection element producing a trace across a portion of the face of said screen indicative of the signals being received during said scanning, means selectively receiving a given frequency during a separate period of the operating cycle of said receiver, and means coupled to said receiver and deflection element for producing a trace across another portion of the face of said screen indicativeof the signal being received at said given frequency during said other period of the operating cycle.

, 5. In a circuit including a receiver on a cathode ray oscilloscope including a beam producing means, a screen and vertical and horizontal deection elements, means cyclically scanning a given frequency band of a given period of the operating cycle of said receiver, means selectively receiving a given frequency in said band during a separate period of the operating cycle of said receiver, means applying a voltage to the horizontal deection plate of said cathode ray tube to sweep the beam in one directionacross the face of said screen during said given period of the operating cycle and to sweep the beam backward in the opposite direction across the face of said screen during said other period of said operating cycle, means applying said scanned received signals to said vertical deection plate to produce a visual indication of the signals being received during said scanning period and during said other period, and means applying a voltage to said vertical deflection plate to displace the trace during said other period of said operating cycle to thereby produce a separate indication of the signal received over said given frequency.

ALBERT PREISMAN.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,347,977 Van Lieshout May 2, 1944 2,381,940 Wallace et al. Aug. 14, 1945 2,412,991 Labin Dec. 24, 1946 

